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V. Dmitrasinovic

Publications and source records attributed to V. Dmitrasinovic.

25 records · Page 2Linked to original sources
arXiv2000

Cubic Casimir operator of SU$_C$(3) and confinement in the nonrelativistic quark model

Only two-body [${\rm F}_{i} \cdot {\rm F}_{j}$] confining potentials have been considered, thus far, in the quark model without gluons, which by construction can only depend on the quadratic Casimir operator of the colour SU(3) group. A three-quark potential that depends on the cubic Casimir operator is added to the quark model. This results in improved properties of $q^3$ colour non-singlet states, which can now be arranged to have (arbitrarily) higher energy than the singlet, and the "colour dissolution/anticonfinement" problem of the ${\rm F}_{i} \cdot {\rm F}_{j}$ model is avoided.

hep-ph↗
arXiv2000

U_A(1) symmetry breaking, scalar mesons and the nucleon spin problem in an effective chiral field theory

We establish a relationship between the scalar meson spectrum and the $U_A (1)$ symmetry-breaking 't Hooft interaction on one hand and the constituent quark's flavor-singlet axial coupling constant $g_{A, Q}^{(0)}$ on the other, using an effective chiral quark field theory. This analysis leads to the new sum rule $g_{A, Q}^{(0)}[m_{η'}^{2} + m_η^{2} - 2 m_{K}^{2} ]\simeq - m_{f_{0}^{'}}^{2} - m_{f_{0}}^{2} + 2 m_{K_{0}^{*}}^{2}$, where $η^{'}, η, K$ are the observed pseudoscalar mesons, $K_{0}^{*}$ is the strange scalar meson at 1430 MeV and $f_{0}, f_{0}^{'}$ are "the eighth and the ninth" scalar mesons. We discuss the relationship between the constituent quark flavor-singlet axial coupling constant $g_{A, Q}^{(0)}$ and the nucleon one $g_{A, N}^{(0)}$ (``nucleon's spin content'') in this effective field theory. We also relate $g_{A, Q}^{(0)}$, as well as the flavour-octet constituent quark axial coupling constant $g_{A, Q}^{(1)}$ to vector and axial-vector meson masses in general as well as in the tight-binding limit.

hep-ph↗
arXiv1999

Composite antisymmetric-tensor Nambu-Goldstone bosons in a four-fermion interaction model and the Higgs mechanism

Starting from the Fierz transform of the two-flavour 't Hooft interaction (a four-fermion Lagrangian with antisymmetric Lorentz tensor interaction terms augmented by an NJL type Lorentz scalar inetraction responsible for dynamical symmetry breaking and quark mass generation), we show that: (1) antisymmetric tensor Nambu-Goldstone bosons appear provided that the scalar and tensor couplings stand in the proportion of two to one, which ratio appears naturally in the Fierz transform of the two-flavour 't Hooft interaction; (2) non-Abelian vector gauge bosons coupled to this system acquire a non-zero mass. Axial-vector fields do not mix with antisymmetric tensor fields, so there is no mass shift there.

hep-th↗
arXiv1999

Pion-nucleon scattering and the nucleon sigma term in an extended sigma model

A modified linear sigma model that allows for $g_A = 1.26$ by addition of vector and pseudovector $πN$ coupling terms was discussed by Bjorken and Nauenberg and by Lee. In this extended linear sigma model the elastic $π$N scattering amplitudes satisfy the relevant chiral low-energy theorems, such as the Weinberg-Tomozawa relation for the isovector scattering length and in some cases Adler's "consistency condition". The agreement of the isospin symmetric $πN$ scattering length with experiment is substantially improved in this extended sigma model as compared with the original one. We show that the nucleon sigma term ($Σ_N$) in the linear- and the extended sigma models with three different kinds of chiral symmetry breaking terms are identical. Within the tree approximation the formal operator expression for the $Σ_N$ term and the value extracted from the $πN$ scattering matrix coincide. Large values of $Σ_N$ are easily obtained without any $s\bar s$ content of the nucleon. Using chiral rotations the Lagrangian of this extended sigma model reproduces the lowest-order $πN$ chiral perturbation theory Lagrangian.

hep-ph↗
arXiv1998

Partially conserved axial current constraints on pion production/absorption within nonrelativistic dynamics

We show the necessity of two-nucleon axial currents and associated pion emission/ absorption operators for the partial conservation of the axial current (PCAC) nuclear matrix elements with arbitrary nuclear dynamics described by a nonrelativistic Schroedinger equation. As examples we construct such nonrelativistic axial two-body currents in the linear- and heterotic (g_A = 1.26) sigma models, with an optional isoscalar vector (omega) meson exchange. The nuclear matrix elements obey PCAC only if the nuclear wave functions used in the calculation are solutions to the Schroedinger equation with the static one-meson-exchange potential constructed in the respective (sigma) model. The same holds true for the nucler pion production amplitude, since it is proportional to the divergence of the axial current matrix element, by virtue of PCAC. Thus we found a new consistency condition between the pion creation/absorption operator and the nuclear Hamiltonian. We present examples drawn from our models and discuss implications for one-pion-two-nucleon processes.

nucl-th↗
arXiv1995

Isospin breaking corrections to nucleon form factors in the constituent quark model

We examine isospin breaking in the nucleon wave functions due to the $u - d$ quark mass difference and the Coulomb interaction among the quarks, and their consequences on the nucleon electroweak form factors in a nonrelativistic constituent quark model. The mechanically induced isospin breaking in the nucleon wave functions and electroweak form factors are exactly evaluated in this model. We calculate the electromagnetically induced isospin admixtures by using first-order perturbation theory, including the lowest-lying resonance with nucleon quantum numbers but isospin 3/2. We find a small ($\leq 1\%$), but finite correction to the anomalous magnetic moments of the nucleon stemming almost entirely from the quark mass difference, while the static nucleon axial coupling remains uncorrected. Corrections of the same order of magnitude appear in charge, magnetic, and axial radii of the nucleon. The correction to the charge radius in this model is primarily isoscalar, and may be of some significance for the extraction of the strangeness radius from e.g. elastic forward angle parity violating electron-proton asymmetries, or elastic ${}^4He({\vec e},e')$ experiments.

hep-ph↗